1. Field of the Invention
This invention relates to a circuit board unit, and more particularly to an improved circuit board unit that executes a self-diagnosis program.
2. Description of the Related Art
Heretofore, in systems employing circuit boards including an electrically rewritable programmable device, there is an internal circuit board in which the read only memory (ROM) of the central processing unit (CPU) mounted on the main body of the system outside of the circuit board is changed, or an external system having another CPU is connected so as to change the program to be down-loaded while communicating with the CPU of the main body of the system. Thereby, the operation of the circuit board of interest can be self-diagnosed.
However, in the construction of such circuit board systems, there is a problem that it requires alot of troublesome labor due to the use of the system connected externally to the circuit board. In addition the problem is presented that the system becomes large in physical size. Further, there is a problem that the program of the circuit board of interest cannot be changed easily, because to satisfy the detailed functions of changing only the program of the programmable device, the processing loads on the other functions such as the control of the main body of the system etc., are heavy. As a result, in many cases, this processing load affects even the system of the main body.